Electrographic printers and copiers utilizing developer comprising toner, carrier, and other components use a developer mixing apparatus and related processes for mixing the developer and toner used during the printing process. The term “electrographic printer,” is intended to encompass electrophotographic printers and copiers that employ dry toner developed on an electrophotographic receiver element, as well as ionographic printers and copiers that do not rely upon an electrophotographic receiver. The electrographic apparatus often incorporates an electromagnetic brush station or similar development station, to develop the toner to a substrate (an imaging/photoconductive member bearing a latent image), after which the applied toner is transferred onto a sheet and fused thereon.
As is well known, a toner image may be formed on a photoconductor by the sequential steps of uniformly charging the photoconductor surface in a charging station using a corona charger, exposing the charged photoconductor to a pattern of light in an exposure station to form a latent electrostatic image, and toning the latent electrostatic image in a developer station to form a toner image on the photoconductor surface. The toner image may then be transferred in a transfer station directly to a receiver, e.g., a paper sheet, or it may first be transferred to an intermediate transfer member or ITM and subsequently transferred to the receiver. The toned receiver is then moved to a fusing station where the toner image is fused to the receiver by heat and/or pressure.
In the electrographic process, a dielectric member, such as a photoconductive element, is initially uniformly electrically charged. The electrostatic latent image charge pattern is formed on the dielectric member by exposing the dielectric member to a suitable exposure source. For example, if the dielectric member is a photoconductive element, the photoconductive element is exposed by an exposure source such as a laser scanner or an LED array. The latent image charge pattern is developed into a visible image by bringing the electrostatic latent image charge pattern into close proximity to a developer material such as contained in a magnetic brush or other known type of development station.
The developer material is typically formed of two or more components that include non-marking, magnetic, carrier particles and marking, non-magnetic toner particles. Because of the triboelectric interaction between the toner and carrier particles, the two types of particles develop charges of opposite polarity and the toner particles electrostatically adhere to the carrier particles. The development station delivers the developer in close proximity to the latent image charge pattern present on the dielectric member and the charged toner particles are attracted to and develop the latent image charge pattern.
Using an electrostatic field to urge the toner particles in the direction of the receiver member subsequently transfers the resulting toner particle developed image to a receiver member, such as paper or plastic sheet. The electrostatic field is commonly applied in one of several ways. For example, charge can be sprayed on the back of the receiver member using a corona device. However, it is frequently preferable to use an electrically biased transfer roller to apply the field. Upon completion of the transfer of the toner particle developed image to a receiver member, the developed image is fused to the receiver member by application of heat and/or pressure.
One of the larger contributors to image quality problems is the variation in environmental conditions that occurs in and around the development station. Warmers, driers, humidifiers and additives have been used to combat and control this problem, all with an eye to controlling the effect of the ambient environment on image quality. U.S. application publication No. 2004/0042815, published on Mar. 4, 2004 shows a humidification system for a development station to control charge on toner particles for developing a latent image charge patterns. Humidification is provided by adding water vapor to an airflow directed into the developer station. The addition of a humidification system is costly and also difficult to control. It would be preferable to have a developer station that did not need a humidification system to maintain image quality through the ambient environment range but instead adjusted a parameter internal to the development subsystem to maintain image quality.